The present invention generally relates to an oil heater of a type having a wick fed radiant burner and, more particularly, to a wick raising and lowering mechanism in the oil heater.
In general, an oil heater having a wick fed radiant burner, the output of which is controllable by raising and lowering the wick, has a problem in that, when the wick once raised towards a maximum combustion position at which the highest burner output is available is excessively lowered in an attempt to adjust the burner output to a minimum value, incomplete combustion of fuel such as, for example, kerosene, is liable to occur accompanied by the emission of a considerable amount of carbon monoxide and other obnoxious exhaust gases.
In order to obviate this problem, a wick raising and lowering mechanism utilizing a one-way stopper operable only during the wick lowering operation and defining a minimum combustion position for the wick at which the lowest possible burner output is available, has been devised and disclosed in, for example, Japanese Laid-open Utility Model Publication No. 56-173808, published in 1981 and corresponding to U.S. Pat. No. 4,424,019 patented Jan. 3, 1984. For the purpose of the discussion of the prior art believed to be closest to the present invention, some of the drawings employed in the above mentioned prior art reference are herein reproduced and numbered FIGS. 6 and 7, reference to which will now be made.
Referring first to FIG. 6 which is a partial transverse sectional view of the prior art oil heater as viewed from top, the wick raising and lowering mechanism, hereinafter referred to as "wick adjustment", comprises a rotary shaft 25 supported for rotation about its own longitudinal axis and also for axial movement between engageable and released positions in a direction perpendicular to a cylindrical wick 21 which is adapted to pass, i.e., helically raised and lowered one at a time, through the annular space between outer and inner wick tubes 22a and 22b, the outer wick tube 22a being supported for helical rotation relative to the inner wick tube 22b and having a plurality of spikes engageable with the wick 21. The wick adjustment also comprises a rack plate 23 curved so as to follow the curvature of the outer wick tube 22a and extending an angular distance about the longitudinal sense of the outer wick tube 22a with its opposite ends exteriorly secured to the outer wick tube 22a. As best shown in FIG. 7, the rack plate 23 has a rack slot defined therein so as to extend obliquely relative to the longitudinal sense of the outer wick tube 22a and having a linear rack defined at 24 for engagement with a pinion gear 26 which is rigidly mounted on the rotary shaft 25 for movement together with the rotary shaft 25. This pinion gear 26 is constantly drivingly engaged with the rack 24 regardless of the position of the rotary shaft in a direction axially thereof, and the rotary shaft 25 is normally urged by a biasing spring 27 to the engageable position as shown in FIG. 6 with its inner end face 25a held in sliding contact with or in proximity of the outer wick tube 22a.
In the construction so far described, the rotation of the shaft 25 and, hence, the pinion 26 in one of the oppsite directions, for example, clockwise as viewed in FIG. 7 results in the raise of the wick 21 from an extinguishing position, at which the top of the wick 21 is completely accommodated within the annular space between the outer and inner wick tubes 22a and 22b, towards the maximum combustion position, together with the outer wick tube 22a. The rotation of the shaft 25 and, hence, the pinion 26 in the other of the opposite directions, i.e., counterclockwise, results in the movement of the wick 21 in a direction reverse to that described above. When and so long as the wick 21 is held at the extinguishing position, one of the rack teeth located at an upper end of the rack 24, that is, the rack tooth identified by 24a, is engaged with the pinion 26 whereas when and so long as the wick 21 is held at the maximum combustion position, the rack tooth 24b located at the other, lower end of the rack 24 is engaged with the pinion 26.
In order to avoid the excessive lowering of the wick 21 towards the extinguishing position past a minimum combustion position at which the burner can give a minimum output with no substantial occurrence of incomplete combustion, that is, without being substantially accompanied by the considerable emission of CO and HC components, the outer wick tube 22a is provided with a sloped projection or lug 28 formed by, for example, lancing a portion of the outer wick tube 22a, which corresponds in position to the minimum combustion position, so as to protrude outwardly of the outer wick tube 22a and into the path of movement of the inner end of the rotary shaft 25 relative to the outer wick tube 22a. This sloped lug 28 is so shaped and so oriented that, during the counterclockwise rotation of the outer wick tube 22a, as viewed in FIG. 6, caused by the clockwise rotation of the rotary shaft 25, the inner end face 25a of the shaft 25 can slide over the sloped lug 28 while the shaft 25 is permitted to axially displace against the biasing spring 27, but during the clockwise rotation of the outer wick tube 22a caused by the counterclockwise rotation of the shaft 25, the inner end of the shaft 25 can be brought into abutment with the sloped lug 28, thereby disabling the continued clockwise rotation of the outer wick tube 22a.
Thus, in the prior art oil heater, while the wick 21 held in the extinguishing position can be moved or raised to the maximum combustion position merely be continuously rotating the rotary shaft 25 in the clockwise direction through a predetermined angle over which the shaft 25 can rotate about its longitudinal axis, the counterclockwise rotation of the shaft 25 starting from the condition in which the wick 21 is held at the maximum combustion position is temporarily interrupted when the inner end of the shaft 25 is brought into abutment with the sloped lug 28 at which time the wick is brought to the minimum combustion position. Therefore, no possibility occurs that the wick is excessively lowered during an attempt to adjust the burner output to a minimum value without incomplete combustion of fuel brought about. However, this merit appears to have created a disadvantage of the prior art oil heater by the following reason.
In order to further lower the wick 21 in the minimum combustion position towards the extinguishing position to extinguish the burner flame, the rotary shaft 25 must be, while an external force necessary to turn it counterclockwise is continuously applied thereto, pulled against the spring 27 to let the inner end of the shaft 25 disengage from the sloped lug 28 and then start sliding relatively down along the slope of the sloped lug 28. This procedure is awkward and inconvenient to follow, and this is particularly true where the wick 21 then held at the maximum combustion position is desired to be lowered to the extinguishing position all the way at a stroke.